The general procedure for the synthesis of pyrazole-3-carboxylic acid from 3-methylpyrazole was as follows: an aqueous solution of potassium permanganate (KMnO4, 40.9 g, 0.26 mol) was slowly added to a stirring solution of 3-methyl-1H-pyrazole (9.8 mL, 0.12 mol) dissolved in 0.5 L of water. The reaction mixture was heated to reflux and maintained for 5 hours. After completion of the reaction, the black suspension was cooled and filtered. The filtrate was concentrated to a smaller volume and acidified with 3 N hydrochloric acid (HCl). Subsequently, the precipitated white solid product was collected and washed with ethyl ether (Et2O) to give the final pyrazole-3-carboxylic acid in 100% yield.
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